1. Field of the Invention
This invention relates to magnetic recording media having a magnetic layer on a non-magnetic support such as, for example, magnetic tapes, magnetic disks and the like, and including as a lubricant a fluorinated sulfo-ester of an organosilane compound.
2. Description of the Prior Art
Magnetic tapes are required to have various characteristics including not only a low coefficient of friction and a smooth and stable traveling performance, but also a minimal amount of powder loss and a good splicing characteristic. When magnetic tapes are used in magnetic recording and reproducing apparatus such as video tape recorders, the tapes are usually run at high speeds in physical contact with tape guides, magnetic heads, and the like. It thus becomes important that the tapes have excellent wear resistance and are capable of traveling in a stable condition over a long period. For example, when the friction coefficient on the tape surface varies at the time of the recording or reproducing, the tape will vibrate at portions of the guides or magnetic heads. This leads to the disadvantage that the recording or reproducing signal, e.g., the audio signal, varies in frequency, resulting in a sound or noise with a frequency different from the original frequency or with a vibration noise of the tape creating the so-called "Q sound" which is distinctly audible.
To overcome this defect, various attempts have been made to provide a good lubricating property to magnetic tapes. For example, it has been common practice to add solid lubricants such as molybdenum disulfide, graphite, or wax to magnetic paints which include a magnetic powder such as gamma-Fe.sub.2 O.sub.3 powder and a vinyl chloride resin binder. However, these solid lubricants have the disadvantage in that they are not effective in improving the durability of the record medium and serve to deteriorate its magnetic characteristics when added in large amounts. On the other hand, higher fatty acids, higher fatty acid esters, paraffin hydrocarbons, and silicone oils (e.g., dimethyl silicone fluid, diphenyl silicone fluid, and the like) can also be used as lubricants. These lubricants, however, do not impart satisfactory durability and lubricating properties and particularly are not adequate for cassette tapes for video tape recorders. In addition, these lubricants tend to exude and bloom on the surface of the magnetic layer, causing a sticking or a stick-slip phenomenon in the magnetic tape.
It will be understood from the above that known lubricants are disadvantageous because the resulting magnetic tapes are rather poor in durability, traveling or running stability, and surface properties, and become unstable especially in still reproduction characteristics as time passes.
In U.S. Pat. No. 4,007,313, owned by the co-assignees of the present invention, there is disclosed a magnetic recording medium including a flexible non-magnetic film base and a magnetic layer which contains or is coated with an organosilicon compound characterized as a fluorinated carboxylic ester of an organosilane compound. This type of lubricant significantly reduces the static friction coefficient and the tendency of the magnetic layer to shed powder. The disclosure of the aforementioned U.S. patent is incorporated into this application by reference.